1. Field of the Invention
The present invention generally relates to peristaltic pumps. More particularly, this invention relates to a peristaltic pump in which the pumping conduit is integrally formed with two portions. The first portion is an occlusive portion that completely occludes when the pressure within this portion is equal to or less than pressure acting on it. The second portion is a non-occlusive portion which is slightly biased so that this portion will be inflated, defining an open passageway, when pressure within it is not substantially less than pressure acting on its outside.
2. Description of the Prior Art
Peristaltic pumps have been used with significant success in a wide range of extracorporeal circulation procedures. Generally, during extracorporeal circulation, blood or other bodily fluids are transferred between a patient and one or more extracorporeal devices which process the fluid before it is returned to the patient. Medical procedures which commonly employ such pumps include, without limitation, the following: open heart surgery, dialysis procedures and long term continuous care situations. During open heart surgery, blood is transferred by the pump between a patient and multiple blood processing devices such as a defoamer, oxygenator and a heater. During dialysis procedures, the pump passes the blood through a dialyzer which removes impurities. In a long term continuous care situation, intravenous solutions are slowly infused by the pump through a venous catheter into the patient, for either general distribution or localized treatment.
Peristaltic pumps can be described as volumetric pumps which include a movable or rotating member having rollers that will compress a flexible pump conduit at spaced apart intervals. The successive of compression of the conduit and the relative movement of this compression point along the length of the conduit, forces the fluid through the conduit. Its simplicity of operation and the absence of direct contact between the pumped fluid and the various pump components are two of the principal advantages of a peristaltic pump.
While used with considerable success, some peristaltic pump designs exhibit certain inherent limitations. Obviously, these limitations must be taken into consideration during the use of the pump. For example, some peristaltic pumps use non-occlusive conduits that are progressively compressed by the rollers against a raceway or stator and are driven by constant speed motors. A non-occlusive conduit has a normally open passageway defined through its center. These pumps draw blood at a substantially constant rate. If the fluid circuit becomes occluded downstream of such a pump, the pump can overpressurize the conduit resulting in rupture. Additionally, if the upstream supply of fluid to the pump stops because of an occlusion, the pump will generate negative pressures downstream of the occlusion. When low enough, the pressure will damage or hemolyze the blood and/or result in the emptying of the fluid supply vessel. If the fluid supply is emptied, the possibility exists for the supply tissue vessel of the patient to collapse, resulting in damage to the tissue at the drainage catheter tip.
Another type of peristaltic pump includes a non-occlusive double walled conduit in which the inner conduit is constructed of thin wall resilient material that can collapse when the pressure acting inside is equal or below the pressure acting outside the conduit. This type of peristaltic pump is described in U.S. Pat. No. 4,515,589. While this pump cannot generate significant negative pressures at their inlets upon upstream occlusion, if the outlet is occluded, overpressurization can result because the conduit is forcefully compressed by the rollers against a raceway or stator.
Another type of peristaltic pump includes an occlusive conduit. These types of pumps are constructed so that when pressure inside of the conduit is equal to or lower than the pressure acting on the outside of the conduit, the conduit will be substantially occluded over its length. One such pump is disclosed in U.S. Pat. No. 5,222,880. While a pump of this variety is incapable of generating negative pressures when the supply of fluid to the pump is stopped, in order to operate and overcome the inherent tension of the tubing, the pump requires inlet fluid pressures and flow rates which, at times, may be greater than that which is desired or available.
In view of the above disadvantages and limitations, it can be seen that there is still a need in the art to provide an improved peristaltic pump which avoids producing negative pressures upstream of the pump inlet, which cannot overpressurize downstream from the pump outlet, and which is capable of filling and pumping a greater amount of blood at a lower inlet pressures compared to pumps that are normally occluded along their length.
It is therefore a principle object of the present invention to provide a peristaltic pump which requires lower inlet pressures in order to fill and pump a significant quantity of blood.
It is another object of the present invention to provide a peristaltic pump which will cease to pump blood when the blood supply filling pressure is equal to or falls below the pressure acting on the outside of the pump inlet.
A further object of the present invention is to provide a peristaltic pump which is unable to generate subatmospheric pressures upstream from the pump inlet.
Still another object of this invention is to provide a peristaltic pump which will cease to pump a fluid when the fluid supply filling pressure is equal to or falls below the pressure acting on the outside of the pump's inlet.
It is also an object of this invention to provide a peristaltic pump which can generate a slight subatmospheric pressure downstream from its inlet when the fluid supply filling pressure is equal to or less than the pressure acting on the outside of the pump chamber.
It is yet another object of this invention to provide a peristaltic pump which is incapable of overpressurizing when the outlet is occluded.
The present invention achieves the above and other objects by providing a peristaltic pump, without a raceway or stator, that uses a pump conduit wrapped under tension around rollers mounted on a rotatable rotor. The pump conduit is made of a resilient material and normally exhibits a slightly biased condition along its length except for a small segment of its length located adjacent to the inlet of the pump. This inlet segment of the pump conduit is formed so that it is completely occluded when the pressure inside the pump conduit is equal to or less than the pressure acting on the outside of the pump conduit. The inlet segment or occlusive portion of the pump conduit begins upstream from the location where the rotating rollers first engage the pump conduit and may or may not extend slightly into the region engaged by the rotating rollers.
When constructed in the above manner, the peristaltic pump will pump blood or another fluid as long as the fluid supply filling pressure is above the pressure acting on the outside of the pump chamber. The fluid will cease to be pumped when the fluid supply or filling pressure is equal to or falls below the pressure acting on the outside of the pump chamber. This occurs even if the rotor of the pump continues to operate and rotate. As a result, negative relative pressures cannot be generated upstream from the occluded inlet segment of the pump conduit. When the occlusive segment is completely occluded, however, the pump can generate, slight subatmospheric pressures downstream from the occlusive segment if the rotor continues to rotate. These slight subatmospheric pressure, however, are insufficient to cause damage to the blood cells.
Another advantage of this pump conduit design is that the pump is capable of filling and pumping more fluid at lower filling pressures in comparison to pumps having pump conduits which are occlusive along their entire length.
Another advantage is that when used with a reservoir located upstream from the peristaltic pump, the present invention would prevent the reservoir emptying and potentially pumping air into a patient.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the present invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings.